Color images are a significant element in today's printing industry. As a result, electronic color printers and color image creation tools have been increasingly developed to obtain color images using electronic printing methods. Much of the color printing is performed using full color, the gamut of colors including tints and shades of the full color spectrum—reds, greens, blues and their combinations.
A significant amount of color printing, however, can be performed using a highlight color. In this type of printing, only two inks are used in the printing process. These inks comprise black and a highlight color (usually red or blue or a custom color). Electronic printers may be designed specifically for highlight color printing. The highlight color printer is generally faster and less expensive than the full color printers because only two inks are processed as opposed to the three or four inks, which must be processed in order to obtain full color images.
The gamut of full colors is a three-dimensional volume which can be represented by a double hexagonal cone. In this representation, shades vary from dark to light as one moves upwards vertically. Tints vary from unsaturated grays to fully saturated colors as one moves out radially. Hues vary as one moves angularly in the horizontal plane.
The gamut of colors available to a highlight printer can be represented by a two-dimensional triangle sliced from the full color double hexagonal cone at the angle of the highlight hue.
Prior attempts to print a full color image on a highlight color printer involved mapping the three-dimensional double hexagonal cone to the two-dimensional triangle. The printer rendered the highlight color image by mapping the full color specification into a limited set of colors that it could produce. In such a mapping, many different colors in the full color space were mapped to the same color in the highlight color space. Information important to the viewer was often lost.
The related art has disclosed printing systems which attempt to provide color images.
Harrington U.S. Pat. No. 4,903,048 discloses color imaging using ink pattern designs in conjunction with registered two-color imaging to form simulated color images. A printing apparatus is described which is used to perform the two-color imaging.
Langdon U.S. Pat. No. 4,761,669 discloses an electrophotographic highlight color printing machine in which printing is done in at least two different colors. Methods for transferring multiple color images simultaneously are disclosed.
While the related art attempts to map a full color image to a highlight color image, it does not recognize that certain information from the full color image should be preserved depending upon how the color is being used and what type of image is being created.